With the projected rapid growth of U.S. adults aged = 65 years, the numbers of falls and fall-related injuries, and the associated costs, will continue t escalate. Based on several decades of research from primarily randomized controlled trials, physical activity has been identified as an important primary prevention strategy for falls. Yet, the specific physical activity components of previous interventions have varied, with most targeting physical activity recommendations for general health benefit, rather than for fall prevention. Further, based on objective physical activity measures, less than 3% of older U.S. adults meet current recommendations. This is an important disconnect that warrants further examination. Also, once a fall occurs, associated physical activity declines may increase risk for subsequent falls. While studies have identified major life changes post falling, none have examined the degree to which physical activity changes after a fall event. The longitudinal study design provides the necessary flexibility to examine these important research gaps. To address these gaps we will conduct a prospective cohort study to examine the bi-directional associations of physical activity and falls, including the dose-response relationship between of objective measures of physical activity (exposure) and risk of falls and injurious falls (outcomes) as well as the impact of fall event(s) (exposure) on subsequent physical activity (outcome). Participants will be drawn from the existing Atherosclerosis Risk in Communities (ARIC) Study who are community dwelling or living independently within senior housing, ambulatory, and without severe/moderate cognitive impairment. This ancillary study will be conducted concurrently with a proposed Parent ARIC Study exam visit. We will prospectively collect: (1) objective measures of physical activity using accelerometers at baseline and every 12 months (3 time points), and (2) the number of falls and injurious falls at baseline and every six months (5 time points) over a 24 month period in this large (n=3,200), diverse cohort of black and white older adults aged 71-93 years. We will also use 30 years of historical ARIC data to examine the impact of mid-life physical activity on fall risk in later-life. To accomplish these goals, we propose the following three specific aims: (1) Determine the dose-response associations between categories of objective measures of physical activity (total activity volume and volume by intensity categories) and risk of falls and injurious falls, and examine if these associations vary by sex, age, and race (2) evaluate the impact of a fall event(s) on subsequent physical activity levels (total activity volume and volume by intensity categories) while considering the modifying effects of fear of falling; and (3) examine the association of trajectories of physical activity from mid- and late-lie with physical activity, physical function and fall risk in later life. This proposed work has important public health significance as it addresses gaps in the literature pertaining to the specific activity dose that confers fall-risk reduction, the impact of falls on subsequent physical activity, and mid- and late-life physical activity on fall risk in later life.